Dynamic and tissue-specific proteolytic processing of chemerin in obese mice

Chemerin is a chemoattractant involved in immunity as well as an adipokine, whose activity is regulated by successive proteolytic cleavages at its C-terminus. Chemerin's C-terminal sequence and its proteolytic cleavage sites are highly conserved between human and mouse, as well as in other species. We produced, purified and characterized different mouse chemerin forms. Ca2+ mobilization assay showed that the EC50 values for mchem161T and mchem157R were 135.8 +/- 158 nM and 71.2 +/- 55.4 nM, respectively, whereas mchem156S and mchem155F had a 20-fold higher potency with an EC50 of 4.6 +/- 1.8 nM and 3.6 +/- 3.0 nM, respectively, likely representing the two physiologically active forms of chemerin. No agonist activity was found for mchem154A. Similar results were obtained in a chemotaxis assay. To identify and quantify the in vivo mouse chemerin forms in biological samples, we developed specific ELISAs for mchem162K, mchem157R, mchem156S, mchem155F and mchem154A, using antibodies raised against peptides from the C-terminus of the different mouse chemerin forms. The prochemerin form, mchem162K, was the major chemerin form in plasma with its increase matching the increase of total plasma chemerin in obese mice. During the onset of obesity in high-fat diet fed mice, mchem156S was elevated in plasma. In contrast, mchem155F was the dominant form in epididymal fat extracts. Our study provides the first direct evidence that mouse chemerin undergoes extensive, dynamic and tissue-specific proteolytic processing in vivo, similar to human chemerin, underlining the importance of measuring individual chemerin forms in studies of chemerin biology in mouse models.